The process of the present invention relates to an improvement in lowering the pour-point of crude oils, i.e., the temperature at which the crude oil undergoes loss of fluidity, by utilizing a bitumen derived from a tar sand. The loss of fluidity occurs when a relatively small percentage of wax contained in the crude oil precipitates in the form of large interlocking crystals. If the crude is to be pipelined through a location where the ambient temperature is less than the crude's natural pour point, one of two measures must be taken. Either the pipeline must be heated or a "pour-point depressant" must be added to the crude. The cost of these measures can be significant, especially in the case of a heated pipeline.
The term "tar sands" (sometimes also referred to as oil sands or bituminous sands) refers to naturally occurring mixtures of bitumen and sand. Tar sands are typically dark brown to black in color depending upon the bitumen content and composition and can be described either as sand grains cemented by bitumen or as sandstone impregnated with bitumen. Two different types of tar sand bitumen are found to exist in nature. The first of these, as typified by Canadian tar sand deposits, has a layer of connate water surrounding the individual mineral particles. Bitumen is attached outside of this connate water layer. The second type, as typified by U.S. tar sand deposits, does not have this layer of connate water, and the bitumen is attached directly to the mineral particles.
The bitumen of tar sand consists of a mixture of a variety of hydrocarbons and heterocyclic compounds. After the bitumen has been separated from the sand, it can be further treated to form a synthetic crude oil suitable for use as a feedstock for the production of gasoline, heating oil, and/or a variety of petrochemicals. The sand component of tar sand is mostly quartz, with minor amounts of other minerals.
Tar sand deposits often occur in the same geographical area as conventional petroleum deposits; tar sand deposits have been found throughout the world, with the exception of Australia and Antarctica. The major known deposits of tar sands are located in Canada, Venezuela, Utah, Europe, and Africa. It is estimated that the Canadian deposit, known as the "Athabasca tar sands", contains nine hundred (900) billion barrels of oil. About sixty-five percent (65%) of all known oil in the world is contained in tar sand deposits or in heavy oil deposits. The Venezuelan deposit of tar sands is estimated to contain approximately seven hundred (700) billion barrels. The United States has twenty-eight (28) billion barrels in its tar sand deposits. Europe has three (3) billion barrels, and Africa has two (2) billion barrels.
Approximately ninety percent (90%) of the known deposits in the United States are located in Utah, with other major deposits being found in California, Kentucky, and New Mexico. Although the twenty-five (25) billion barrels of bitumen located in Utah may seem small in comparison to the Canadian and Venezuelan deposits, Utah tar sands represent a significant energy resource when compared to crude oil reserves in the United States, which are estimated to be approximately thirty-one (31) billion barrels.
The tar sands located in the Athabasca deposit differ considerably from those deposits located in Utah and other areas of the world. Analysis of the Athabasca tar sands indicate that the average bitumen content is approximately twelve to thirteen percent (12-13%) by weight. The bitumen content of the Utah tar sands, on the other hand, varies from about five percent (5%) to about thirteen percent (13%) by weight, with the average of all deposits being slightly less than ten percent (10%) bitumen by weight.
In any event, due to the remote nature of most tar sand deposits, it is desirable to effect minimal upgrading of the tar sands on-site.
It has now been surprisingly discovered that either raw bitumen or hydrotreated bitumen can be utilized as a crude oil pour-point depressant. This discovery is especially useful where bitumen products need to be transported to a refinery for upgrading, where climatic considerations are important, i.e., ambient temperatures below crude pour point, and where tar sand deposits and crude pipelines are in close proximity. The transport of raw bitumen or hydrotreated bitumen to an existing refinery is desirable since most tar sand occurrences are in remote areas. While it is known that bitumen can be transported in a pipeline with natural gas condensate acting as a diluent, the present invention in contradistinction deals with the addition of bitumen or hydrotreated bitumen to a full boiling range crude oil wherein such addition surprisingly results in the reduction of the pour point of the final blend.
Accordingly, the present invention provides for a method of reducing the pour point of crude oils to be pipelined while concomitantly providing for the transportation of the raw or hydrotreated bitumen to refineries for further upgrading.